2009/3/17 Chas. Owens <chas.ow...@gmail.com>:
> On Tue, Mar 17, 2009 at 09:30, Dermot <paik...@googlemail.com> wrote:
> snip
>> if ($x{$x}) inspects the key's value, not simply the existence of a key?
> snip
>
> Yes, but beware of autovivification (i.e. the creating of keys by
> trying to look at their values). You are safe with this simple case,
> but when dealing with HoHs or other complex data structures you can
> accidentally create keys. Always use exists on each level but the
> last before examining the value of a deeper level. Also, it tests the
> value not the definededness, so if $x{$x} was 0 or '' it would be
> false even though it was defined.
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
> use Data::Dumper;
>
> my %h = (
> english => [ qw/zero one two three/ ],
> latin => [ qw/zerum uno duos tres/ ],
> );
> print Dumper \%h;
>
> #wrong
> unless (defined $h{german}[0]) {
> print "german 0 is not set\n";
> }
>
> #right
> unless (exists $h{chinese} and exists $h{chinese}{mandarin} and
> defined $h{chinese}{mandarin}[0]) {
> print "mandarin chinese 0 is not set\n";
> }
Thanx Chas,
It's compound `exists`, starting from the highest level down until you
get to the depth of the value where you can start using defined.
Thanx,
Dp.
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